I have 97 s10 Blazer the radio comes on shows stereo reception but no sound comes out of any speaker. Tried a differenr radio same results all wires on back are connnected. If i jump a speaker on to the speaker wires coming right off the back of the radio I get sound. I have checked continuity on the speaker wires to the wires coming out of the radio and all shows to be an open circuit. My question is Is ther another plug somwhere or is there an amplifier on this system